Hollow World is a campaign settingboxed set detailing the enormous hollow inside of the planet of Mystara, and the people and creatures that inhabit the lands found there.[1]
Hollow World was written by Aaron Allston, with a cover by Fred Fields and interior illustrations by Thomas Baxa and Mark Nelson, and was published by TSR in 1990 as a boxed set containing a 128-page book, a 64-page book, and a 32-page book, and four large color maps.[1]